Ultrasonic reflux system for one-step purification of carbon nanostructures

ABSTRACT

Reflux systems and methods for purifying carbon nanostructures using same are provided. The reflux system includes a solvent flask, an extraction tube connected to the solvent flask by a siphon tube and a vapor tube each extending between the extraction tube and the solvent flask, and an energy application disposed around the bottom portion of the extraction tube. The reflux systems can be used in a one-step method of purifying carbon nanostructures that includes placing a soot sample that contains the carbon nanostructures and amorphous carbon in a filter and disposing the filter in the extraction tube.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Document No.2000-375043 filed on Dec. 8, 2000, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a reflux systems, and methods, forpurifying carbon nanostructures. More particularly, the presentinvention relates to improved apparatusses and systems and methods ofusing same to purify carbon nanostructures, including single wallnanotubes (SWNTs), multi-wall nanotubes (MWNTs), fullerenes, endohedralmetallofullerenes, carbon nanofibers, and other carbon-containingnano-materials. The reflux systems and methods are particularly usefulfor purifying SWNTs.

One known method of purifying carbon nanostructures includes baking asoot sample at 750° C. in air for about thirty minutes. See“Purification of nanotubes” by Ebbesen et al, Nature, vol. 367, 10February 1994, p. 519. However, Ebbesen's method is directed to thepurification of MWNTs; such high heat in this process tends to damage,or even destroy, SWNTs.

Other known methods of purifying carbon nanostructures involve multiplesteps carried out in multiple apparatuses. See “Purification Procedurefor Single-Walled Nanotubes” by K. Tohji et al., J. Phys. Chem. B, vol.101, 1997, p. 1974-1978, for example. That is, soot produced byarc-discharge includes many byproducts such as metal particles,fullerenes, buckyonions, and a large amount of amorphous carbon togetherwith the desired SWNTs. Thus, heretofore, many steps carried out inmultiple apparatuses have been necessary for purifying SWNTs. The stepstypically include, for example, hydrothermally initiated dynamicextraction (HIDE), sonication, filtration, drying, washing, heattreatment, and acid treatment. But many of the processes are performedin different apparatuses, thereby necessitating removal of the sootsample from one apparatus and placing it in another apparatus.

Still other known methods include microfiltration, and some even useultrasound to assist in the filtration. See “Purification of single-wallcarbon nanotubes by ultrasonically assisted filtration” by Konstantin B.Shelimov et al., Chem. Phys. Lett., vol. 282, 1998, p. 429-434, forexample. In such methods, however, multiple steps are still necessary,and the yield remains low. That is, the soot is first suspended intoluene and filtered to extract soluble fullerenes. Then, thetoluene-insoluble fraction is re-suspended in methanol and filtered withassistance of an ultrasonic horn inserted into the filtration funnel.Finally, a separate acid wash is performed to remove metal particles.Therefore, because of the many steps and apparatuses necessary, thesemethods have been implemented mainly for diluted and relatively pure rawmaterials such as those synthesized by laser ablation; they areinefficient for large quantities of low-purity raw materials.

Lastly, a dilute nitric acid reflux technique has been performed topurify SWNTs. See “A Simple and Complete Purification of Single-WalledCarbon Nanotube Materials”, by Anne C. Dillon et al., Advanced Materials1999, vol. 11, no. 16, p. 1354-1358. But this process still requiresthree steps—including an oxidation step in which the carbon is heated to550° C.—carried out in different apparatuses. Therefore, this processsuffers the same drawbacks as like processes discussed above. Namely,the different steps require transference of the soot, the heating stepdamages or destroys SWNTs, and the method is effective only forhigh-purity soot.

Because the related art purification methods include multiple steps,performed in multiple apparatuses, these methods are time consuming andlabor intensive. Additionally, there is risk that some of the sample islost, contaminated, or destroyed in transit from one apparatus toanother. Further, because of the large amount of amorphous carbon in thesoot samples, and the heating steps, these methods have only been ableto achieve a low yield (about 5 wt %) of 95% pure SWNTs.

SUMMARY OF THE INVENTION

The present invention relates to improved reflux systems and methods forpurifying carbon nanostructures. For example, the present invention canavoid using heat, especially high heat, to purify carbon nanostructuresbecause such high heat tends to damage the carbon nanostructures. Infact, high heat tends to destroy SWNTs altogether, whereas it merelytends to burn off the outer layers of MWNTs.

The present invention can provide methods and apparatuses that areuseful for purifying large quantities of low-purity raw materials, suchas those synthesized by arc-discharge. The present invention can alsopurify such materials in a highly efficient manner which yields a highpercentage of the desired carbon nanostructures.

Still further, the present invention can provide apparatuses and methodsthat are simple and less complex in design and construction by whichvarious forms of carbon nanostructures can be purified. That is, thepresent apparatus and method can be used to purify carbon nanotubes,extract fullerenes, or both, from a given soot sample.

In order to avoid using heat to purify carbon nanostructures, thepresent invention is carried out at ambient, or room temperatureaccording to an embodiment. When purifying carbon nanotubes, anoxidizing gas is introduced into the soot sample in order to oxidize theamorphous carbon therein, and a solvent is used to remove the oxidizedamorphous carbon. When purifying fullerenes, the amorphous carbon is notoxidized but, instead, a solvent is used to remove the fullerenes fromthe soot sample. In any case, because the carbon nanostructures arepurified at ambient temperature, they are not damaged by high heat.Further, the use of little, or no, heat leads to an increased yield ofcarbon nanostructures, especially SWNTs, because the carbonnanostructures are not destroyed in the purification process.

In order to avoid transferring the soot sample between apparatuses,thereby reducing the time required for purification as well as reducingthe risk of contaminating or damaging a sample, the methods of thepresent invention can be performed in a single apparatus. That is, thesoot sample and products separated therefrom can remain in one apparatusuntil the desired structures are purified. Further, because the presentinvention does not require soot transference, it is less labor intensiveand, therefore, less costly.

In order to increase the yield of the desired carbon nanostructurespecially SWNTs—from low-purity raw materials, the present method andapparatus use a one-step process in an embodiment. In the one-stepprocess, amorphous carbon is oxidized, oxidized amorphous carbon isremoved, and metallic particles are removed, in a short period of timebecause these processes are carried out by the same apparatus.Additionally, the processes can be performed simultaneously therebyfurther increasing the speed of the process. Moreover, energy—such asultrasonic vibrations, or microwaves, for exampl—can be used to assistin dispersing agglomerations thereby making more of the soot sampleavailable to the other processes and, hence, make the process moreefficiently attain a higher yield. The ultrasonic energy is applied withthe soot remaining in the same apparatus, and may be applied at the sametime as the other processes, thereby reducing the time necessary topurify the sample. Because the time for purification is reduced, arelatively large, low-purity, sample efficiently can be purified.

A reflux system including a solvent flask, an extraction tube connectedto the solvent flask by a siphon tube and a vapor tube each extendingbetween the extraction tube and the solvent flask, and an energyapplicator disposed around the bottom portion of the extraction tube isprovided pursuant to an embodiment of the present invention. Further, acondenser is connected to the top portion of the extraction tube. Asupply tube is connected to the extraction tube, whereby material can beintroduced into the extraction tube. The reflux system is used in aone-step method, of purifying carbon nanostructures, including placing asoot sample—containing the carbon nanostructures and amorphous carbon—ina filter and disposing the filter in the extraction tube. Solvent isthen introduced into the extraction tube so as to collect in the lowerportion thereof, and remove one of the amorphous carbon and the carbonnanostructures from the soot. Further, the energy applicator is used toapply ultrasonic vibrations to the soot so as to disperse agglomerationstherein. The solvent, and the one of the amorphous carbon and carbonnanostructures dissolved therein, is then removed from the extractiontube so that the other one of the amorphous carbon and the carbonnanostructures remains in the filter. Further, the method is performedat ambient temperature, an oxidizing gas is introduced into theextraction tube to oxidize the amorphous carbon, and acid is introducedinto the extraction tube to remove metallic particles from the soot.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic, partial cross sectional, view showing a refluxsystem according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to reflux systems and methodsfor purifying carbon nanostructures.

The reflux system of the present invention in an embodiment allowscarbon nanostructures to be purified in one step by filtration,extraction, or both, carried out at ambient temperature. That is, sootcontaining the desired carbon nanostructures as well as unwantedbyproducts is put into a filter, is placed into the reflux system and,through various processes performed in the reflux system, the desiredcarbon nanostructures are removed from the reflux system. Therefore,neither the soot, nor any intermediate products, need be removed fromthe reflux system until the purification process is complete; the entirepurification process takes place within the reflux system and takesplace at ambient temperature. The reflux system includes an extractor 1,a condenser 20, and an energy applicator 30.

The extractor 1 includes a solvent flask 2, a thermal mantle 4, and anextraction tube 7. The solvent flask 2 sits in the thermal mantle 4 soas to be heated thereby. The thermal mantle 4 is configured so that itcan produce a variable amount of heat for evaporating various solventsheld within the solvent flask 2. Additionally, the solvent flask 2 has aflask inlet 3 through which solvent, and gases, can be introduced intothe flask 2. A vapor tube 5 and a siphon tube 11 are connected betweenthe solvent flask 2 and the extraction tube 7, so that the solvent flask2 and extraction tube 7 are in communication with one another.

The extraction tube 7 includes a top portion 7′ and a bottom portion 7″.A stopper 8 is disposed in the extraction-tube top portion 7′ so as toform a vapor chamber 9 in the extraction tube 7. The vapor tube 5 isconnected to the extraction tube 7 so as to be in communication with thevapor chamber 9, whereas the siphon tube 11 is connected to the bottomportion 7″ of the extraction tube 7. Spacers 12 are disposed between thevapor tube 5 and the siphon tube 11, as well as between the siphon tube11 and the extraction tube 7. Additionally, a supply tube 13 isconnected to the bottom portion 7″ of the extraction tube 7. The supplytube 13 allows material, in particular gases used during a filtrationprocess, to be introduced into the extraction tube 7. Spacers 12 arealso disposed between the supply tube 13 and the extraction tube 7. Theextraction tube 7 is sized and configured to hold a filter 10 therein.The filter 10 initially holds the sample to be purified and, after thepurification process, holds the undissolved portion of the sample.

The condenser 20 is connected to the upper portion 7′ of the extractiontube 7 so as to receive vapors from the vapor chamber 9. Moreparticularly, the condenser 20 includes a condenser tube 21 having acondenser-tube inlet 22 and a condenser-tube gas outlet 23. Thecondenser-tube inlet 22 is connected to the stopper 8 so as tocommunicate with the vapor chamber 9. The condenser-tube gas outlet 23allows some gases to escape from the top of the condenser tube 21.Further, the condenser tube 21 includes a cooling-fluid jacket 24 havinga cooling-fluid inlet 25 and a cooling-fluid outlet 26.

The energy applicator 30 is disposed about the bottom portion 7″ of theextraction tube 7 so as to apply energy to a sample disposed in filter10. The energy applicator 30 can be, for example, an ultrasonicvibrator, or a microwave applicator. The energy applicator 30 assists indispersing agglomerations in the sample disposed in filter 10 so thatthe sample is more easily, and thoroughly, purified. That is, the energyapplicator 30 allows the apparatus to achieve a higher purity, higheryield, of desired product from the sample.

A general purification process, using the above-described reflux system,will now be described according to an embodiment of the presentinvention.

First, a sample to be purified is placed in the filter 10 which, inturn, is disposed within the extraction tube 7. A solvent, for removingthe soluble portion of the sample, is disposed in the solvent flask 2wherein it is heated so as to evaporate. The evaporated solvent entersevaporation tube 5, which is insulated by vapor-tube insulation 6 so asto maintain the solvent in its evaporated state as it travels throughthe evaporation tube 5. The evaporated solvent then travels through theevaporation tube 5, along the direction of arrow A, so as to enter thevapor chamber 9. In order to assist in driving the evaporated solventthrough the evaporation tube 5, gas may be pumped through the flaskinlet 3. After driving the evaporated solvent to the evaporation chamber9 and, subsequently, to the condenser tube 21, the gas is allowed toexit through the condenser-tube gas outlet 23.

Vapor from vapor chamber 9 enters the condenser-tube inlet 22 and passesup through the condenser tube 21, wherein it is condensed. Thecondensate then falls back through the condenser-tube inlet 22 and downonto the filter 10 disposed in the extraction tube 7. The condensatecollects in the extraction tube 7 and enters the filter 10 so as toreact with the soluble portion of the sample contained therein. When thesolvent level in the extraction tube 7 rises above the highest portionof the siphon tube 11, the solvent then flows through the siphon tube11, in the direction of arrow B, back down into the solvent flask 2carrying the soluble portion of the sample with it. Because the siphontube 11 is connected to the bottom portion 7″ of the extraction tube 7,substantially all of the solvent—including soluble portions of thesample dissolved therein—are removed from the extraction tube 7.

The evaporation process is again carried out as necessary, so that thesoluble portion of the sample is collected in the solvent flask 2. Thatis, the temperature of the thermal mantle is selected so that only thesolvent, not the soluble portion of the sample, is evaporated from thesolvent flask 2.

In order to assist with separating the desired portion of the samplefrom the impurities, gases or other materials may be introduced into theextraction tube 7 through supply tube 13. Generally, gase—such asoxidizing gases, acid vapor and the like—will be introduced and,therefore, the supply tube 13 is connected to the bottom portion 7″ ofthe extraction tube 7 so that the gasses flow up through the filter 10and through the sample contained therein. Further, any unused portion ofthe gases introduced through the supply tube 13 are allowed to exitthrough the condenser-tube gas outlet 23. Although the supply tube 13preferably is connected to the bottom portion 7″, it can be connectedanywhere along the extraction tube 7, especially if liquids are to beintroduced therethrough.

To further assist with separating the desired portion of the sample fromthe impurities, the energy applicator 30 may be used to apply energy tothe sample contained in filter 10. For example, the energy applicator 30may be an ultrasonic vibrator which assists purification by dispersingagglomerated portions of the sample through agitation. The energyapplicator may be used continuously or intermittently throughout thepurification process.

When the desired portion of the sample is that which is soluble, it iscollected in the solvent flask 2 together with solvent. In such a case,the solvent flask can be disconnected from the extraction tube, thesolvent evaporated, and the desired portion of the sample easily iscollected. Further, the undissolved portions of the sample, which may beeither wanted or unwanted, are then collected in the filter 10. When thedesired portion of the sample is that which has not been dissolved, suchis retained in the filter 10, and easily is removed.

Next, a purification process for obtaining carbon nanotubes, and inparticular SWNTs, will be described. In order to carry out a one-steppurification of SWNTs, the reflux system of the present inventionaccording to an embodiment combines the functions of ultrasoundagitation, low temperature oxidation, and instant filtration.

First, a soot sample to be purified is placed in the filter 10 which, inturn, is disposed within the extraction tube 7. The soot sample containsthe desired carbon nanostructures—SWNTs in this example—along with oneor more of the following: amorphous carbon; metal catalyst particles;fullerenes; and other carbon nanoparticles. A solvent, for removingoxidized amorphous carbon from the sample, is disposed in the solventflask 2 wherein it is heated so as to evaporate. In this example, asolvent having a dipole moment larger than one is used to assist indispersing agglomerations in the soot and so as to easily dissolve andloosen oxidized amorphous carbon. Preferably, the dipole moment of thesolvent is in the range of from greater than or equal to about 1, toabout 4. Examples of solvent which may be used include water (H₂O),DMSO, dimethylformamide (DMF), THF, the like and suitable combinationsthereof.

The evaporated solvent enters evaporation tube 5, and then travelsthrough the evaporation tube 5, along the direction of arrow A, so as toenter the vapor chamber 9. In order to assist in driving the evaporatedsolvent through the evaporation tube 5, gas may be pumped through theflask inlet 3. For example, the gas pumped through the flask inlet 3 maybe air or oxygen. After driving the evaporated solvent to theevaporation chamber 9 and, subsequently, to the condenser tube 21, thegas is allowed to exit through the condenser-tube gas outlet 23,although some gas may remain in the extraction tube 7. In either case,when oxygen is used, it assists in oxidizing amorphous carbon.

Solvent vapor from vapor chamber 9 enters the condenser-tube inlet 22and passes up through the condenser tube 21, wherein it is condensed.The solvent condensate then falls back through the condenser-tube inlet22 and down onto the filter 10 disposed in the extraction tube 7.

In order to oxidize the amorphous carbon portion of the sample, anoxidizing agent—such as oxidizing gases, for example, oxygen (O₂) orozone (O₃), or oxidizing liquids, for example, H₂O₂—is introduced intothe extraction tube 7 through supply tube 13. The gasses flow up throughthe filter 10 and through the sample contained therein to oxidize theamorphous carbon. The oxidizing agent may be continuously orintermittently introduced to the extraction tube. The oxidized amorphouscarbon is then carried with the solvent through the siphon tube 11 andinto the solvent flask 2, as described below. Any unused portion of theoxidizing gasses, which were introduced through the supply tube 13, areallowed to exit through the condenser-tube gas outlet 23. Becauseoxidizing gases are introduced into the extraction tube 7, and to thesample in filter 10, heat is not necessary to oxidize the amorphouscarbon. That is, the purification process of the present invention canbe carried out at low temperatures such as, for example, ambient or roomtemperature. By carrying out the purification process at ambienttemperature, the SWNTs and other carbon nanostructures are not damaged,or destroyed, as they are at high temperatures. Further, althoughoxidizing gas has been disclosed, an oxidizing liquid such as H₂O₂ maybe used. However, oxidizing gas is preferred because the oxidizingliquid takes up more volume in the extraction tube and, therefore, thereis less volume available for the solvent.

In order to remove the metal catalyst portions of the sample, acid vaporis introduced into the extraction tube 7 through the supply tube 13. Theacid vapor may be introduced along with the oxidizing gasses, or may beintroduced either before or after the oxidizing gasses. As the acidvapor enters the extraction tube 7 and, thus, the soot sample in filter10, it reacts with the metal particles in the sample thereby formingmetal salts. The type of acid used depends on the solvent used. Acid maybe contained in the solvent and, thus, may be disposed in the solventflask 2. That is, if only the acid and the solvent can co-evaporate,they may be disposed in the solvent flask 2, evaporated, and condensedtogether. Introducing the acid and solvent together is preferable, aslong as the acid does not have a tendency to react with, or decomposein, the solvent vapor which may be hot. In still another embodiment, theacid may be introduced as vapor through the flask inlet 3 and, thereby,also may be used to assist in driving solvent vapor through the vaportube 5. Each of the above three manners of introducing acid to theextraction tube may be used either separately, or in combination withone or more of the other manners of introducing acid to the extractiontube. Further, the acid may be continuously, or intermittently,introduced.

To further assist with separating the desired portion of the sample fromthe impurities, the energy applicator 30 may be used to apply energy tothe sample contained in filter 10. For example, the energy applicator 30may be an ultrasonic vibrator which assists purification by dispersingagglomerated portions of the sample, which agglomerations includeamorphous carbon, metal catalyst particles, and the desired SWNTs. Forexample, ultrasonic vibration of about 100 W to about 1000 W, preferablyabout 350 W to about 500 W, can be applied to the soot sample. Bydispersing the agglomerations, the solvent, and acid vapor, readily canreact with more of the sample and, thus, a higher purity can beachieved. That is, because the agglomerations are dispersed into smallerparticles, a greater surface area is available for the solvent,oxidizing agent, and acid. The energy applicator 30 may be operatedcontinuously, or intermittently, throughout the purification process.

The solvent condensate, received from the condenser, collects in theextraction tube 7 and enters the filter 10 so as to dissolve theoxidized amorphous carbon portion of the sample. The solvent also washesout of the sample any fullerenes that are present. When the solventlevel in the extraction tube 7 rises above the highest portion of thesiphon tube 11, the solvent then flows through the siphon tube 11, inthe direction of arrow B, back down into the solvent flask 2 carryingthe oxidized amorphous carbon, and metal salt, portions of the samplewith it. Because the siphon tube 11 is connected to the bottom portion7″ of the extraction tube 7, substantially all of the solvent—includingthe oxidized amorphous carbon, and metal salt, portions of the samplecontained therein—are removed from the extraction tube 7.

The evaporation process is again carried out as necessary, so that theoxidized amorphous portion of the sample is collected in the solventflask 2. That is, the temperature of the thermal mantle is selected sothat only the solvent and acid are evaporated from the solvent flask 2,leaving the amorphous carbon, metal salts, and fullerenes in the solventflask 2. What is left in the solvent flask 2, however, depends on whatwas included in the soot sample first placed in filter 10. That is, ifno fullerenes were present in the original soot sample, then none willbe present in the solvent flask 2. Similarly, if there were no metalcatalyst particles in the original soot sample, then there will be nometal salts in the solvent flask 2. But if there were fullerenes in theoriginal soot sample, they are collected in the solvent flask 2 andeasily may be extracted therefrom. That is, the apparatus can purify asample containing both carbon nanotubes and fullerenes, and can do sosuch that both structures are purified at the same time. When purifyingcarbon nanotubes and fullerenes at the same time, it is preferable tofirst use a solvent with a dipole less than about 1, before introducingan oxidizing agent to the sample, to increase the yield of fullereneswhich may be damaged by the oxidizing agent.

In order to retain the desired SWNTs in the filter 10, a filter having apore size of less than about 1 μm is used. Such pore size allowsfullerenes, but not nanotubes, to pass therethrough. Additionally, thefilter may be made of any material that will withstand attack from theacid introduced to remove the metal catalyst particles. For example, thefilter may be made of Teflon, or paper fiber which is stable in an acidenvironment. Further, preferably, the filter 10 is one which encloses,or envelopes, the soot sample so that no carbon nanotubes are washed outwhen the solvent is removed from the extraction tube 7.

Thus, in the above one-step purification process, the desired SWNTs arefiltered and left in the filter 10, whereas any fullerenes are extractedand are present in the solvent flask 2. The process is a one-stepprocess in that the soot sample, and/or intermediate products therefrom,do not need to be removed from one apparatus until purification of thedesired carbon nanostructures contained in sample is complete.

The above described method, for purifying SWNTs, may also be used topurify MWNTs, or any other carbon nanotubes or nano-fibers. All that isnecessary to purify these other structures is to have them in theoriginal soot sample which is placed in the filter 10. That is, if theoriginal soot sample contains MWNTs, such structures will be collectedin the filter 10, whereas fullerenes, amorphous carbon, and metal saltswill be collected in solvent flask 2. Similarly, if the original sootsample contains other carbon nanotubes, or nano-fibers, these structureswill be purified and collected in the filter 10. However, at present,the filter 10 does not distinguish between SWNTs, MWNTs, othernanotubes, or other nano-fibers. Therefore, any of such structures whichare present in the original soot sample will be collected in the filter10.

In one example of the above-described process for purifying SWNTsaccording to an embodiment of the present invention, water was used forthe solvent, and HNO₃ was used as the acid. The acid was mixed with thewater in the solvent flask 2 before heating it. The water and HNO₃ werethen evaporated together, and condensed together. Oxygen gas wascontinuously introduced through flask inlet 3 at about 50 ml/min toassist in driving the solvent and acid vapor through the vapor tube 5.Also, a flow of oxygen gas containing about 2% of ozone was introducedto the extraction tube 7 through supply tube 13 at about 50 ml/min.Thus, the oxidizing agent for this example includes oxygen and ozonegasses, wherein the content of ozone was limited to about 2% of the gasintroduced through supply tube 13 because if the concentration of ozoneis too high, it may destroy the SWNTs. The energy applicator was anultrasonic vibrator operated at 350 W, and was operated continuouslythroughout the purification process. All of the previously describedconditions—heating and vapor condensation of both H₂O and HNO₃ together,introduction of gasses through both flask inlet 3 and supply tube 13,and ultrasonic vibration—were carried out simultaneously. For a 10 gsoot sample, produced by an arc-discharge operation, containing at leastSWNTs, amorphous carbon, metal catalyst particles, and a trace amount offullerenes, the above process was carried out under the previouslydescribed conditions for about 3 to about 4 hours, and resulted in a 95wt % yield of SWNTs having a purity of 95%. This yield, at such a highpurity of SWNTs, is believed to be greater than has been achieved ascompared to known processes, thus exemplifying the advantages of thepresent invention. Although specific process parameters have been givenhere, they are not intended to be limiting to the scope of the presentinvention. For example, these parameters may be varied in accordancewith the guidance given throughout the specification.

The present invention in an embodiment is also applicable to theextraction of fullerenes. That is, the apparatus and method of thepresent invention in an embodiment may be used to purify an originalsoot sample mainly containing fullerenes as the desired product. In sucha case, the above-described apparatus is used in the above-describedmanner, except that: no oxidizing gasses are introduced; no acid vaporis introduced; an inert gas may be used to drive the solvent vaporthrough the vapor tube 5; the extraction tube has an inert gasenvironment; and a solvent having a dipole less than about 1 is usedpursuant to an embodiment of the present invention. Such solventsinclude, for example, CS₂, toluene, benzene the like, and suitablecombinations thereof. By using a solvent with a dipole less than about1, the solvent readily extracts the fullerenes from the sample whileleaving the amorphous carbon and metallic particles in the filter.Further, because the amorphous carbon is not oxidized, and because themetal catalyst particles are not reacted with acid, such products arecontained in the filter 10 along with any carbon nanotubes that werepresent in the original soot sample. Thus, only the solvent andfullerenes are collected in the solvent flask 2 thereby making it easyto collect the desired fullerenes.

It is contemplated that numerous modifications may be made to the refluxsystem and purification method of the present invention withoutdeparting from the spirit and scope of the invention as defined in theclaims. For example, although the reflux system was described as beingused to purify carbon nanostructures, it can be used in the same manneras a traditional SOXLET extractor to purify, or extract, any desiredsubstance from a given sample.

Because the process is carried out at ambient temperature, with littleor no heating of the soot sample, SWNTs are not damaged or destroyedthereby producing an increased yield of SWNTs. Additionally, because theprocess in an embodiment is carried out in one apparatus—i.e., it is aone-step process—it can be done quickly, at a reduced cost, with reducedrisk of contaminating or damaging the sample. Further, the apparatussystems and method of the present invention are capable of efficientlypurifying large amounts of low-purity soot to a high degree with a highyield of the desired carbon nanostructures. Moreover, the presentinvention in an embodiment can be used easily to purify carbonnanotubes, fullerenes, or other suitable substances.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

Description of Reference Numerals

-   -   1 extractor    -   2 solvent flask    -   3 flask inlet    -   4 thermal mantle    -   5 vapor tube    -   6 vapor-tube insulation    -   7 extraction tube    -   7′ top portion of extraction tube    -   7″ bottom portion of extraction tube    -   8 stopper    -   9 vapor chamber    -   10 filter    -   11 siphon tube    -   12 spacers    -   13 supply tube    -   20 condenser    -   21 condenser tube    -   22 condenser-tube inlet    -   23 condenser-tube gas outlet    -   24 cooling-fluid jacket    -   25 cooling-fluid inlet    -   26 cooling-fluid outlet    -   30 energy applicator

1-31. (canceled)
 32. A reflux system comprising: a solvent supplydevice; an extraction tube connected to the solvent supply device,wherein the extraction tube has a top portion and a bottom portion; asiphon tube extending from the bottom portion of the extraction tube,and connected to the solvent source; and an energy applicator disposedaround the bottom portion of the extraction tube.
 33. The reflux systemaccording to claim 32, wherein the solvent supply device is a solventflask, and the reflux system further comprises a vapor tube connectedbetween the solvent flask and the extraction tube.
 34. The reflux systemaccording to claim 33, further comprising a condenser connected to thetop portion of the extraction tube.
 35. The reflux system according toclaim 33, further comprising a supply tube connected to the extractiontube through which material can be introduced into the extraction tube.36. The reflux system according to claim 32, wherein the energyapplicator is an ultrasonic vibrator.
 37. A reflux system comprising: asolvent source including a solvent flask and a vapor tube connected tothe solvent flask; an extraction tube having a top portion and a bottomportion, wherein the extraction tube is connected to the vapor tubeallowing the extraction tube to be in communication with the solventflask; a condenser connected to the top portion of the extraction tube,wherein the condenser is in communication with the vapor tube; a siphontube extending from the bottom portion of the extraction tube, andconnected to the solvent flask; and a supply tube connected to theextraction tube through which material can be introduced into theextraction tube.
 38. The reflux system according to claim 37, furthercomprising an energy applicator disposed around the bottom portion ofthe extraction tube.
 39. The reflux system according to claim 38,wherein the energy applicator is an ultrasonic vibrator.
 40. A one-stepmethod of purifying carbon nanotubes, comprising: placing a soot samplethat contains the carbon nanotubes together with amorphous carbon in afilter and disposing the filter in a lower portion of an extractiontube; introducing an oxidizing agent into the extraction tube to oxidizethe amorphous carbon; introducing a solvent into the extraction tube soas to contact the filter, collect in the lower portion of the extractiontube, and dissolve the oxidized amorphous carbon from the soot sample;and removing the solvent from the extraction tube allowing the carbonnanotubes to remain in the filter, wherein the method of purifyingcarbon nanotubes is carried out at ambient temperature.
 41. The methodaccording to claim 40, wherein the soot sample includes metal catalystparticles, and the method further comprises introducing acid into theextraction tube allowing the acid to remove the metal catalyst particlesfrom the soot sample.
 42. The method according to claim 41, wherein thestep of introducing an oxidizing agent includes introducing oxidizinggas, the step of introducing acid into the extraction tube includesintroducing acid vapor, and further wherein the acid vapor issimultaneously introduced with the oxidizing gas.
 43. The methodaccording to claim 41, wherein the step of introducing solvent includesintroducing solvent vapor to the extraction tube and condensing thesolvent vapor, and wherein the step of introducing acid into theextraction tube includes introducing acid vapor along with the solventvapor.
 44. The method according to claim 40, further comprising applyingenergy to the soot sample so as to disperse agglomerations.
 45. Themethod according to claim 44, wherein the energy is ultrasonicvibration.
 46. The method according to claim 45, wherein the step ofapplying energy is performed simultaneously with the step of introducingan oxidizing agent and simultaneously with the step of introducingsolvent.
 47. The method according to claim 40, wherein the solvent has adipole greater than or equal to about
 1. 48. A one-step method ofpurifying carbon nanostructures, comprising: placing a soot sample thatcontains the carbon nanostructures in combination with amorphous carbonin a filter and disposing the filter in a lower portion of an extractiontube; introducing solvent into the extraction tube so as to contact thefilter, collect in the lower portion of the extraction tube, anddissolve one of the amorphous carbon and the carbon nanostructures fromthe soot sample; applying energy to the soot sample in the extractiontube so as to disperse agglomerations; and removing the solvent, and theone of the amorphous carbon and carbon nanostructures dissolved therein,from the extraction tube so that the other one of the amorphous carbonand the carbon nanostructures remains in the filter.
 49. The methodaccording to claim 48, wherein the step of applying energy includesapplying ultrasonic vibration.
 50. The method according to claim 48,further comprising carrying out the method of purifying carbonnanostructures at ambient temperature.
 51. The method according to claim48, further comprising introducing an oxidizing agent into theextraction tube to oxidize the amorphous carbon.
 52. The methodaccording to claim 51, wherein the step of introducing solvent includesintroducing a solvent having a dipole greater than or equal to about 1so that the carbon nanostructures remain in the filter, whereas theoxidized amorphous carbon is dissolved in the solvent.
 53. The methodaccording to claim 51, further comprising introducing acid into theextraction tube to remove metallic particles from the soot sample. 54.The method according to claim 53, wherein the step of introducing anoxidizing agent includes introducing an oxidizing gas, wherein the stepof introducing acid into the extraction tube includes introducing acidvapor, and wherein the acid vapor is introduced simultaneously with theoxidizing gas.
 55. The method according to claim 53, wherein the step ofintroducing solvent to the extraction tube includes introducing solventvapor into the extraction tube and condensing the solvent vapor, andwherein the step of introducing acid into the extraction tube includesintroducing acid vapor along with the solvent vapor.
 56. The methodaccording to claim 48, wherein the step of introducing solvent includesintroducing a solvent having a dipole less than about 1, so that thecarbon nanostructures are dispersed in the solvent, whereas theamorphous carbon remains in the filter.
 57. The method according toclaim 56, wherein the step of introducing solvent includes introducingsolvent vapor with an inert gas, and then condensing the solvent vapor.58. A one-step method of purifying carbon fullerenes, comprising:placing a soot sample that contains the carbon fullerenes together withamorphous carbon in a filter and disposing the filter in a lower portionof an extraction tube; introducing a solvent into the extraction tube soas to contact the filter, collect in the lower portion of the extractiontube, and form a solution with the fullerenes from the soot sample,wherein the solvent has a dipole moment less than about 1; and removingthe solvent containing the fullerenes from the extraction tube so thatthe amorphous carbon remains in the filter, wherein the above steps arecarried out at ambient temperature.
 59. The method according to claim58, further comprising applying ultrasonic energy to the soot sample soas to disperse agglomerations.
 60. The method according to claim 59,wherein the step of applying energy is performed simultaneously with thestep of introducing solvent.
 61. The method according to claim 58,wherein the step of introducing solvent includes evaporating the solventfrom a flask, causing the solvent to travel along an evaporation tube toa condenser, and condensing the evaporated solvent in the condenser sothat the solvent is introduced to the extraction tube, and wherein thestep of removing the solvent includes returning the solvent to theflask.
 62. The method according to claim 61, wherein the step ofintroducing solvent includes using an inert gas to assist in causing theevaporated solvent to travel along an evaporation tube, and furthercomprising maintaining an atmosphere, in the extraction tube, withoutoxidizing agents.